As a measure to design a three-dimensional structure by using a computer, three-dimensional CAD has been used. By using three-dimensional CAD, furniture product can be three-dimensionally designed with desired dimensions and shape on a screen. Further, data of a furniture product designed by using three-dimensional CAD can be produced as NC data by using CAD/CAM so that members of the furniture product can be machined by using NC (numerical control) machining tools.